Light-sensitive material containing silver halide, reducing agent and polymerizable compound

ABSTRACT

A light-sensitive material comprises a support and a light-sensitive layer which contains a reducing agent, an ethylenic unsaturated polymerizable compound and silver halide grains having a halogen composition composed of two or more halogens including iodine. The silver halide grains have a core/shell structure, and at least 50% of the silver halide grains have an aspect ratio of not more than 5. The silver iodide content in the shell is higher than that in the core. An image-forming method utilizing the light-sensitive material is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/218,180 filed Sept.15, 1988, now abandoned, which is a continuation-in-part application ofU.S. patent application Ser. No. 07/012,462 filed on Feb. 9, 1987, nowabandoned.

FIELD OF THE INVENTION

This invention relates to a light-sensitive material comprising alight-sensitive layer containing silver halide, a reducing agent and apolymerizable compound provided on a support, and further relates to animage-forming method employing the light-sensitive material.

BACKGROUND OF THE INVENTION

A light-sensitive material which comprises a support and alight-sensitive layer containing silver halide, a reducing agent and apolymerizable compound can be used in an image forming method in which alatent image of silver halide is formed, and then the polymerizablecompound is polymerized to form the corresponding image.

Examples of said image forming methods are described in Japanese PatentPublication Nos. 45(1970)-11149 (corresponding to U.S. Pat. No.3,697,275), 47(1972)-20741 (corresponding to U.S. Pat. No. 3,687,667)and 49(1974) -10697. and Japanese Patent Provisional Publication Nos.57(1982)-138632, 57(1982)-142638, 57(1982)-176033, 57(1982)-211146(corresponding to U.S. Pat. No. 4,557,997), 58(1983)-107529(corresponding to U.S. Pat. No. 4,560,637), 58(1983)-121031(corresponding to U.S. Pat. No. 4,547,450) and 58(1983)-169143. In theseimage forming methods, when the exposed silver halide is developed usinga developing solution, the polymerizable compound is induced topolymerize in the presence of a reducing agent (which is oxidized) toform a polymer image. Thus, these methods need a wet development processemploying a developing solution. Therefore the process takes arelatively long time.

An improved image forming method employing a dry process is described inJapanese Patent Provisional Publication Nos. 61(1986)-69062 and61(1986)-73145 (the contents of both publications are described in U.S.Pat. No. 4,629,676 and European Patent Provisional Publication No.0174634A2). In this image forming method, a recording material (i.e.,light-sensitive material) comprising a light-sensitive layer containinga light-sensitive silver salt (i.e., silver halide), a reducing agent, across-linkable compound (i.e., polymerizable compound) and a binderprovided on a support is imagewise exposed to form a latent image, andthen the material is heated to polymerize within the area where thelatent image of the silver halide has been formed. The above methodemploying the dry process and the light-sensitive material employablefor such method are also described in Japanese Patent ProvisionalPublication Nos. 61(1986)-183640, 61(1986)-188535 and 61(1986)-228441(the content of the three publications are shown in U.S. patentapplication Ser. No. 827,702).

The above-mentioned image forming methods are based on the principle inwhich the polymerizable compound is polymerized within the area where alatent image of the silver halide has been formed.

Further, Japanese Patent Provisional Publication No. 61(1986)-260241(corresponding to U.S. patent application Ser. No. 854,640) describesanother image forming method in which the polymerizable compound withinthe area where a latent image of the silver halide has not been formedis polymerized. In this method, when the material is heated, thereducing agent functions as polymerization inhibitor within the areawhere a latent image of the silver halide has been formed, and thepolymerizable compound in the other area is polymerized.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light-sensitivematerial (or element) which gives a clear image.

There is provided by the present invention a light-sensitive elementcomprising a support and a light-sensitive layer which contains silverhalide grains, a reducing agent and an ethylenic unsaturatedpolymerizable compound, said silver halide grains being contained insuch amount that the total silver content in the light-sensitive layeris in the range of from 0.1 mg/m² to 10 g/m², said reducing agent beingcontained in the range of from 0.1 to 1,500 mole % based on the totalsilver content in the light-sensitive layer, and said polymerizablecompound being contained in the range of from 5 to 120,000 times byweight as much as the amount of the silver halide grains,

wherein the silver halide grains have a mean grain size of 0.001 to 5 μmand at least 50% of number of the silver halide grains have an aspectratio of not more than 5 and have such a core/shell structure that theshell portion contains iodine at a concentration higher than that in thecore portion, the iodine concentration in the shell portion is not lessthan 10 mole % of the halogen content therein, and the shell portioncontains silver in an amount of 0.01 to 50 weight % of the silver in thesilver halide grains.

The light-sensitive material of the invention can be advantageously usedin a process which comprises the steps of:

imagewise exposing to light the light-sensitive element to form a latentimage of the silver halide; and

heating the light-sensitive element either simultaneously with or afterthe imagewise exposure to polymerize the polymerizable compound withinthe area where the latent image of the silver halide has been formed (orthe area where the latent image of the silver halide has not beenformed).

The light-sensitive material of the invention is characterized in thatat least 50% of number of the silver halide grains have an aspect ratioof not more than 5 and have such a core/shell structure that the iodineconcentratin in the shell portion is higher than that in the coreportion.

The present inventor has found that the light-sensitive materialemploying the above-mentioned silver halide grains is reduced in theoccurrence of fog and accelerated in the development. Therefore, thelight-sensitive material of the invention can form a clear image havinga high maximum density and a low minimum density.

DETAILED DESCRIPTION OF THE INVENTION

The silver halide grains in the present invention have a halogencomposition composed of two or more halogens including iodine. Forinstance, silver chloroiodide, silver iodobromide or silverchloroiodobromide grain is employed in the invention. The silver halidegrain consists essentialy of silver halide. In more detail, at least 90weight % (more preferably 95 weight %, and most preferably 99 weight %)of the silver halide grain comprises the above-mentioned two or morekinds of the silver halide.

Further, at least 50% of number of the silver halide grains have anaspect ratio of not more than 5. According to study of the presentinventor, the silver halide grains having an aspect ratio of not morethan 5 (non-tabular grains) are preferably used in the above-mentionedlight-sensitive material. The process for preparation of thelight-sensitive material is much more complicated than that of theconventional silver halide photographic material. Accordingly, tabulargrains having an aspect ratio of more than 5 should be carefully used inthe process for preparation of the light-sensitive material, since thetabular grains are fragile. Further, in the case that thelight-sensitive material employs microcapsules, it is difficult toincorporate the tabular silver halide grains into the microcapsules(especially, into the shell of the microcapsules).

The aspect ratio of the silver halide grains means tha ratio of thegrain size (diameter), namely the ratio of the tabular plane to thethickness. The grains size means the diameter of the circle having thesame area as the projected area of the grain on the tabular plane. It ismore preferred that at least 70% of the silver halide grains have anaspect ratio of not more than 5. It is also preferred that the silverhalide grains have an average aspect ratio of not more than 5. Each ofthe above proportions, "50%" and "70%" means the proportion of of thetotal projected area of the non-tabular grains having an aspect ratio ofnot more than 5 to that of all of the grains.

There is no specific limitation on the crystal habit of the silverhalide grain, except that at least 50% of the silver halide grains havean aspect ratio of not more than 5. Accordingly, ususal silver halidegrains, such as cubic grains and octahedral grains may be used in thepresent invention. Further, it is preferred that at least 50% of numberof the silver halide grains has an "aspect ratio" of not more than 5with respect to not only thickness but also various directions.

Furthermore, the silver halide grain in the invention has a core/shellstructure. In the present specification, "core/shell structure" means astructure in which the halogen composition in the silver halide grain isnot uniform from the center to the surface of the grain.

Example of the silver halide grain having the core/shell structure is agrain having a multilayer structure formed in the grain formation, whichis described in Japanese Patent Provisional Publication Nos.57(1982)-154232, 58(1983)-108533, 59(1984)-48755 and 59(1984)-52237,U.S. Pat. No. 4,433,048 and European Patent No. 100,984. Another exampleof the silver halide grain is a grain having a multilayer structureformed by adding a different halogen ion to a silver halide grain havinga uniform halogen composition to convert the surface halogen compositionof the grain, which is described in Japanese Patent ProvisionalPublication No. 52(1977)-18309 and U.S. Pat. Nos. 3,622,318 and3,703,584.

The multilayer structure of the grain generally is a double layerstructure. In the case that the silver halide grain has the double layerstructure, the outer part is referred to as "shell", and the inner partis referred to as "core" in the specification.

The silver halide grain can have a triple or more layer structure. Inthis case, the outermost layer is referred to as "shell", and all ofother portions are referred to as "core".

The shell portion contains silver in an amount of 0.01 to 50 weight % ofthe silver in the silver halide grains. The shell preferably containssilver in an amount of 0.1 to 50 weight %.

Further, the silver halide grain can have a structure in which thehalogen composition continuously changes from the center to the surfaceof the grain, in addition to the multilayer structure. In this case, theouter portion in which 50 wt. % of silver is present is referred to as"shell", and the other inner portion is referred to as "core".

In these core/shell structures, the iodine content (concentration) inthe shell is higher than that in the core in the present invention. Theiodine content in the shell is preferably at least 2 mole % (morepreferably 10 mole %) higher than that in the core.

There is no specific limitation with respect to the other halogencontents (i.e. the chlorine content and the bromine content). Generally,the bromine content is preferably higher than the chlorine content tomore reduce the occurrence of fog.

The iodide content (per the total halogen) in the shell is not less than10 mole % (preferably not less than 30 mole %). The silver iodidecontent in the whole silver halide grain preferably is not more than 50mole %.

Two or more kinds of silver halide grains which differ in crystal habit,grain size, and/or other features from each other can be used incombination.

The silver halide grains have a mean grain (or particle) size of 0.001to 5 μm, more preferably 0.001 to 2 μm, most preferably 0.01 to 0.5 μm.

The total silver content (including silver halide and an organic silversalt which is one of optional components) in the light-sensitive layeris in the range of from 0.1 mg/m² to 10 g/m². The silver content of thesilver halide in the light-sensitive layer preferably is not more than 1g/m², more preferably in the range of from 1 mg to 500 mg/m².

The silver halide grain can be prepared, for instance by the followingprocess.

The silver halide grain is preferably prepared in the form of a silverhalide emulsion. Various processes for the preparation of the silverhalide emulsion are known in the conventional technology for thepreparation of photographic materials.

The silver halide grain having the core/shell structure can be formed bygrowing a different silver halide on a silver halide grain having auniform halogen composition to coat the grain with the different silverhalide. The silver halide grain having the core/shell structure can bealso formed by adding a different halogen ion to a silver halide grainhaving a uniform halogen composition to modify the surface halogencomposition of the grain. These processes can be repeated to form atriple or more layer structure.

In thess processes, the relation between the halogen compositions in thecore and the shell is adjusted to form a silver halide grain in whichthe silver iodide content in the shell is higher than that in the core.

The silver halide emulsion can be prepared by the acid process, neutralprocess or ammonia process. In the stage for the preparation, a solublesilver salt and a halogen salt can be reacted in accordance with thesingle jet process, double jet process or a combination thereof. Areverse mixing method, in which grains are formed in the presence ofexcess silver ions, or a controlled double jet process, in which a pAgvalue is maintained constant, can be also employed. In order toaccelerate grain growth, the concentrations or amounts or the silversalt and halogen salt to be added or the rate of their addition can beincreased as described in Japanese Patent Provisional Publication Nos.55(1980)-142329 and 55(1980) -158124, and U.S. Pat. No. 3,650,757, etc.

The silver halide emulsion may be of a surface latent image type thatforms a latent image predominantly on the surface of silver halidegrains, or of an inner latent image type that forms a latent imagepredominantly in the interior of the grains. A direct reversal emulsioncomprising an inner latent image type emulsion and a nucleating agentmay be employed. The inner latent image type emulsion suitable for thispurpose is described in U.S. Pat. Nos. 2,592,250 and 3,761,276, JapanesePatent Publication No. 58(1982)-3534 and Japanese Patent ProvisionalPublication No. 57(1982)-136641, etc. The nucleating agent that ispreferably used in combination with the inner latent image type emulsionis described in U.S. Pat. Nos. 3,227,552, 4,245,037, 4,255,511,4,266,013 and 4,276,364, and West German Patent Provisional Publication(OLS) No. 2,635,316.

In the preparation of the silver halide emulsions, hydrophilic colloidsare advantageously used as protective colloids. Examples of usablehydrophilic colloids include proteins, e.g., gelatin, gelatinderivatives, gelatin grafted with other polymers, albumin, and casein;cellulose derivatives, e.g., hydroxyethyl cellulose, carboxymethylcellulose, cellulose sulfate, etc.; saccharide derivatives, e.g., sodiumalginate and starch derivatives; and a wide variety of synthetichydrophilic polymers, such as polyvinyl alcohol, polyvinyl alcoholpartial acetal, poly-N-vinylpyrrolidone, polyacrylic acid,polymethacrylic acid, polyacrylamide, polyvinylimidazole, andpolyvinylpyrazole, and copolymers comprising monomers constituting thesehomopolymers. Among them, gelatin is most preferred. Examples ofemployable gelatins include not only lime-processed gelatin, but alsoacid-processed gelatin and enzyme-processed gelatin. Hydrolysis productsor enzymatic decomposition products of gelatin can also be used.

In the formation of silver halide grains in the silver halide emulsion,ammonia, an organic thioether derivative as described in Japanese PatentPublication No. 47(1972)-11386 or sulfur-containing compound asdescribed in Japanese Patent Provisional Publication No. 53(1978)-144319can be used as a silver halide solvent. Further, in the grain formationor physical ripening, a cadmium salt, a zinc salt, a lead salt, athallium salt, or the like can be introduced into the reaction system.Furthermore, for the purpose of overcoming high or low intensityreciprocity law failure, a water-soluble iridium salt, e.g., iridium(III) or (IV) chloride, or ammonium hexachloroiridate, or awater-soluble rhodium salt, e.g., rhodium chloride can be used.

After the grain formation or physical ripening, soluble salts may beremoved from the resulting emulsion by a known noodle washing method ora sedimentation method. The silver halide emulsion may be used in theprimitive condition, but is usually subjected to chemical sensitization.Chemical sensitization can be carried out by the sulfur sensitization,reduction sensitization or noble metal sensitization, or a combinationthereof that are known for emulsions for the preparation of theconventional light-sensitive materials.

When the sensitizing dyes are added to the silver halide emulsion, thesensitizing dye is preferably added during the preparation of theemulsion as described in Japanese Patent Application No.60(1986)-139746.

The reducing agent, the polymerizable compound and the support whichconstitute the light-sensitive material of the invention with the silverhalide grains are described below. Thus composed material is referredhereinafter to as "light-sensitive material".

The reducing agent employed in the light-sensitive material has afunction of reducing the silver halide and/or a function of acceleratingor restraining a polymerization of the polymerizable compound. Examplesof the reducing agents having these functions include various compounds,such as hydroquinones, catechols, p-aminophenols, p-phenylenediamines,3-pyrazolidones, 3-aminopyrazoles, 4-amino-5-pyrazolones,5-aminouracils, 4,5-dihydroxy-6-aminopyrimidines, reductones,aminoreductones, o- or p-sulfonamidophenols, o- orp-sulfonamidonaphthols, 2-sulfonamidoindanones,4-sulfonamido-5-pyrazolones, 3-sulfonamidoindoles,sulfonamidopyrazolobenzimidazoles, sulfonamidopyrazolotriazoles,α-sulfonamidoketones, hydrazines, etc. Depending on the nature or amountof the reducing agent, the polymerizable compound in either the areawhere a latent image of the silver halide has been formed or the areawhere a latent image of the silver halide has not been formed can bepolymerized. For example, when a hydrazine derivative is used as thereducing agent, the polymerizable compound is polymerized within thearea where the latent image has been formed. In the other developingsystem, in which the polymerizable compound within the area where thelatent image has not been formed is polymerized, 1-phenyl-3-pyrazolidoneis preferably employed as the reducing agent.

The light-sensitive materials employing the reducing agent having thesefunctions (including compounds referred to as developing agent orhydrazine derivative) are described in Japanese Patent ProvisionalPublication Nos. 61(1986)-183640, 61(1986)-188535 and 61(1986)-228441,and Japanese Patent Application Nos. 60(1985)-210657, 60(1985)-226084,60(1985)-227527 and 60(1985)-227528. These reducing agents are alsodescribed in T. James, "The Theory of the Photographic Process", 4thedition, 291-334 (1977), Research Disclosure No. 17029, 9-15 (June1978). and Research Disclosure No. 17643, 22-31 (December 1978). Thereducing agents described in the these publications and applications canbe employed in the light-sensitive material of the present invention.Thus, "the reducing agent(s)" in the present specification means toinclude all of the reducing agents described in the above mentionedpublications and applications.

These reducing agents can be used singly or in combination. In the casethat two or more reducing agents are used in combination, certaininteractions between these reducing agents may be expected. One of theinteractions is for acceleration of reduction of silver halide (and/oran organic silver salt) through so-called super-additivity. Otherinteraction is for a chain reaction in which an oxidized state of onereducing agent formed by a reduction of silver halide (and/or an organicsilver salt) induces or inhibits the polymerization of the polymerizablecompound via oxidation-reduction reaction with other reducing agent.Both interactions may occur simultaneously. Thus, it is difficult todetermine which of the interactions has occurred in practical use.

Examples of these reducing agents include pentadecylhydroquinone,5-t-butylcatechol, p-(N,N-diethylamino)phenol,1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone,1-phenyl-4-methyl-4-heptadecylcarbonyloxymethyl-3-pyrazolidone,2-phenylsulfonylamino-4-hexadecyloxy-5-t-octylphenol,2-phenylsulfonylamino-4-t-butyl-5-hexadecyloxyphenol,2-(N-butylcarbamoyl)-4-phenylsulfonylaminonaphtol,2-(N-methyl-N-octadecylcarbamoyl)-4-sulfonylaminonaphthol,1-acetyl-2-phenylhydrazine, 1-acetyl-2-(p- or o-aminophenyl)hydrazine,1-formyl-2-(p- or o-aminophenyl)hydrazine, 1-acetyl-2-(p- oro-methoxyphenyl)hydrazine, 1-lauroyl-2-(p- or o-aminophenyl)hydrazine,1-trityl-2-(2,6-dichloro-4-cyanophenyl)hydrazine,1-trityl-2phenylhydrazine. 1-phenyl-2-(2,4,6-trichlorophenyl)hydrazine,1-{2-(2,5-di-tert-pentylphenoxy)butyloyl}-2-(p- oro-aminophenyl)hydrazine, 1-{2-(2,5-di-t-pentylphenoxy)butyloyl-2-(p- oro-aminophenyl)hydrazine pentadecylfluorocaprylate salt, 3-indazolinone,1-(3,5-dichlorobenzoyl)-2-phenylhydrazine,1-trityl-2-[{(2-N-butyl-N-octylsulfamoyl)-4-methanesulfonyl}-phenyl]hydrazine,1-{4-(2,5-di-tert-pentylphenoxy)butyloyl}-2-(p- or o-methoxyphenyl)hydrazine,1-(methoxycarbonylbenzohydryl)-2-phenylhydrazine, 1-formyl-2-[4-{2-(2,4-di-tert-pentylphenoxy)butylamid}phenyl]hydrazine,1-acetyl-2-[4-{2-(2,4-di-tert-pentylphenoxy)butylamido}phenyl]hydrazine,1-trityl-2-[{2.0-dichloro-4-(N,N-di-2-ethylhexyl)carbamoyl}phenyl]hydrazine,1-(methoxycarbonylbenzohydryl)-2-(2,4-dichlorophenyl)hydrazine and1-trityl-2-[(2-(N-ethyl-N-octylsulfamoyl)-4-methanesulfonyl}phenyl]hyrazine.

The amount of the reducing agent in the light-sensitive layer rangesfrom 0.1 to 1,500 mole % based on the amount of silver (contained in theabove-mentioned silver halide and an organic silver salt).

There is no specific limitation with respect to the polymerizablecompound, except that the polymerizable compound has an ethylenicunsaturated group. Any known ethylenic unsaturated polymerizablecompounds including monomers, oligomers and polymers can be contained inthe light-sensitive layer. In the case that heat development (i.e.,thermal development) is utilized for developing the light-sensitivematerial, the polymerizable compounds having a relatively higher boilingpoint (e.g., 80° C. or higher) that are hardly evaporated upon heatingare preferably employed. In the case that the light-sensitive layercontains a color image forming substance, the polymerizable compoundsare preferably cross-linkable compounds having plural polymerizablegroups in the molecule, because such cross-linkable compounds favorablyserve for fixing the color image forming substance in the course ofpolymerization hardening of the polymerizable compounds.

Examples of compounds having an ethylenic unsaturated group includeacrylic acid, salts of acrylic acid, acrylic esters, acrylamides,methacrylic acid, salts of methacrylic acid, methacrylic esters,methacrylamide, maleic anhydride, maleic esters, itaconic esters,styrene, styrene derivatives, vinyl ethers, vinyl esters, N-vinylheterocyclic compounds, allyl ethers, allyl esters, and compoundscarrying a group or groups corresponding to one or more of thesecompounds.

Concrete examples of the acrylic esters include n-butyl acrylate,cyclohexyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, furfurylacrylate, ethoxyethoxy acrylate, dicyclohexyloxyethyl acrylate,nonylphenyloxyethyl acrylate, hexanediol diacrylate, butanedioldiacrylate, neopentylglycol diacrylate, trimethylolpropane triacrylate,pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate,diacrylate of polyoxyethylenated bisphenol A, polyacrylate ofhydroxypolyether, polyester acrylate, and polyurethane acrylate.

Concrete examples of the methacrylic esters include methyl methacrylate,butyl methacrylate, ethylene glycol dimethacrylate, butanedioldimethacrylate, neopentylglycol dimethacrylate, trimethylolpropanetrimethacrylate, pentaerythritol trimethacrylate, pentaerythritoltetramethacrylate, and dimethacrylate of polyoxyalkylenated bisphenol A.

The polymerizable compounds can be used singly or in combination of twoor more compounds. Further, compounds formed by bonding a polymerizablegroup such as a vinyl group or a vinylidene group to a reducing agent ora color image forming substance are also employed as the polymerizablecompounds. The light-sensitive materials employing these compounds whichshow functions as both the reducing agent and the polymerizablecompound, or of the color image forming substance and the polymerizablecompound are included in embodiments of the invention.

The amount of the polymerizable compound for incorporation into thelight-sensitive layer ranges from 5 to 1.2×10⁵ times (by weight) as muchas the amount of silver halide, more preferably from 10 to 1×10⁴ timesas much as the silver halide.

The light-sensitive material of the invention can be prepared byarranging a light-sensitive layer containing the above-mentionedcomponents on a support. There is no limitation with respect to thesupport. In the case that heat development is utilized in the use of thelight-sensitive material, the material of the support preferably isresistant to heat given in the processing stage. Examples of thematerial employable for the preparation of the support include glass,paper, fine paper, coat paper, synthetic paper, metals and analoguesthereof, polyester, acetyl cellulose, cellulose ester, polyvinyl acetal,polystyrene, polycarbonate, polyethylene terephthalate, and paperlaminated with resin or polymer (e.g., polyethylene).

Various embodiments of the light-sensitive materials, optionalcomponents which may be contained in the light-sensitive layer, andauxiliary layers which may be optionally arranged on the light-sensitivematerials are described below.

The polymerizable compound is preferably dispersed in the form of oildroplets in the light-sensitive layer. A light-sensitive material inwhich the polymerizable compound is dispersed in the form of oildroplets is described in Japanese Patent Application No.60(1985)-218603. Other components in the light-sensitive layer, such assilver halide, the reducing agent, the color image forming substancesmay be also contained in the oil droplets. A light-sensitive material inwhich silver halide is contained in the oil droplets is described inJapanese Patent Application No. 60(1985)-261888.

The oil droplets of the polymerizable compound ar preferably prepared inthe form of microcapsules. There is no specific limitation onpreparation of the microcapsules. The light-sensitive material in whichthe oil droplets are present in the form of a microcapsule is describedin Japanese Patent Application No. 60(1985)-117089. There is also nospecific limitation on shell material of the microcapsule, and variousknown materials such as polymers which are employed in the conventionalmicrocapsules can be employed as the shell material. It is preferredthat at least 70 weight % (more preferably at least 90 weight %) of thesilver halide grains are arranged in the shell of the microcapsules oron the inner surface of the shell of the microcapsules. The mean size ofthe microcapsule preferably ranges from 0.5 to 50 μm, more preferably 1to 25 μm, most preferably 3 to 20 μm.

The light-sensitive layer can further contain optional components suchas color image forming substances, sensitizing dyes, organic silversalts, various kinds of image formation accelerators, thermalpolymerization inhibitors, thermal polymerization initiators,development stopping agents, fluorescent brightening agents,discoloration inhibitors, antihalation dyes or pigments, antiirradiationdyes or pigments, matting agents, antismudging agents, plasticizers,water releasers and binders.

There is no specific limitation with respect to the color image formingsubstance, and various kinds of substances can be employed. Thus,examples of the color image forming substance include both coloredsubstance (i.e., dyes and pigments) and non-colored or almostnon-colored substance (i.e., color former or dye- or pigment-precursor)which develops to give a color under application of external energy(e.g., heating, pressing, light irradiation, etc.) or by contact withother components (i.e., developer). The light-sensitive material usingthe color image forming substance is described in Japanese PatentProvisional Publication No. 61(1986)-73145.

Examples of the dyes and pigments (i.e., colored substances) employablein the invention include commercially available ones, as well as variousknown compounds described in the technical publications, e.g., YukiGosei Kagaku Kyokai (ed.), Handbook of Dyes (in Japanese, 1970) andNippon Ganryo Gijutsu Kyokai (ed.), New Handbook of Pigments (inJapanese, 1977). These dyes and pigments can be used in the form of asolution or a dispersion.

Examples of the substances which develop to give a color by certainenergy includes thermochromic compounds, piezochromic compounds,photochromic compounds and leuco compounds derived from triarylmethanedyes, quinone dyes, indigoid dyes, azine dyes, etc. These compounds arecapable of developing a color by heating, application of pressure,light-irradiation or air-oxidation.

Examples of the substances which develop to give a color in contact withother components include various compounds capable of developing a colorthrough some reaction between two or more components, such as acidbasereaction, oxidation-reduction reaction, coupling reaction, chelatingreaction, and the like. Examples of such color formation systems aredescribed in Hiroyuki Moriga, "Introduction of Chemistry of SpecialityPaper" (in Japanese, 1975), 29-58 (pressure-sensitive copying paper),87-95 (azo-graphy), 118-120 (heat-sensitive color formation by achemical change) or in MSS. of the seminer promoted by the Society ofKinki Chemical Industry, "The Newest Chemistry of ColoringMatter--Attractive Application and New Development as a FunctionalColoring Matter", 26-32 (June, 19, 1980). Examples of the colorformation systems specifically include a color formation system used inpressure-sensitive papers, etc., comprising a color former having apartial structure of lactone, lactam, spiropyran, etc., and an acidicsubstance (developer), e.g., acid clay, phenol, etc.; a system utilizingazo-coupling reaction between an aromatic a diazonium salt, diazotate ordiazosulfonate and naphthol, aniline, active methylene, etc.; a systemutilizing a chelating reaction, such as a reaction betweenhexamethylenetetramine and a ferric ion and gallic acid, or a reactionbetween a phenolphthalein-complexon and an alkaline earth metal ion; asystem utilizing oxidation-reduction reaction, such as a reactionbetween ferric stearate and pyrogallol, or a reaction between silverbehenate and 4-methoxy-1-naphthol, etc.

The color image forming substance in the light-sensitive material ispreferably used in an amount of from 0.5 to 50 parts by weight, and morepreferably from 2 to 30 parts by weight, per 100 parts by weight of thepolymerizable compound. In the case that the developer is used, it ispreferably used in an amount of from about 0.3 to about 80 parts byweight per one part by weight of the color former.

There is no specific limitation with respect to the sensitizing dyes,and known sensitizing dyes used in the conventional art of photographymay be employed in the light-sensitive material of the invention.Examples of the sensitizing dyes include methine dyes, cyanine dyes,merocyanine dyes, complex cyanine dyes, complex merocyanine dyes,holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxonoldyes. These sensitizing dyes can be used singly or in combination.Combinations of sensitizing dyes are often used for the purpose ofsupersensitization. In addition to the sensitizing dyes, a substancewhich does not per se exhibit spectral sensitization effect or does notsubstantially absorb visible light but shows supersensitizing activitycan be used. The amount of the sensitizing dye to be added generallyranges from about 10⁻⁸ to about 10⁻² mol per 1 mol of silver halide.

The sensitizing dye is preferably added during the stage of thepreparation of the silver halide emulsion. The light-sensitive materialwherein the sensitizing dye has been added during the silver halidegrain formation is described in Japanese Patent Application No.60(1985)-139746. The examples of the sensitizing dye are also describedin above Japanese Patent Application No. 60(1985)-139746.

When the heat development is employed in the use of the light-sensitivematerial, an organic silver salt is preferably contained in thelight-sensitive material. It can be assumed that the organic silver salttakes part in a redox reaction using a silver halide latent image as acatalyst when heated to a temperature of 80° C. or higher. In such case,the silver halide and the organic silver salt preferably are located incontact with each other or close together. Examples of organic compoundsemployable for forming such organic silver salt include aliphatic oraromatic carboxylic acids, thiocarbonyl group-containing compoundshaving a mercapto group or an α-hydrogen atom, imino group-containingcompounds, and the like. Among them, benzotriazoles are most preferable.The organic silver salt is preferably used in an amount of from 0.01 to10 mol., and preferably from 0.01 to 1 mol., per 1 mol. of thelight-sensitive silver halide. Instead of the organic silver salt, anorganic compound (e.g., benzotriazole) which can form an organic silversalt in combination with an inoganic silver salt can be added to thelight-sensitive layer to obtain the same effect. The light-sensitivematerial employing an organic silver salt is described in JapanesePatent Application No. 60(1985)-141799 (corresponding to U.S. patentSer. No. 879,747).

Various image formation accelerators are employable in thelight-sensitive material of the invention. The image formationaccelerators have a function to accelerate the oxidation-reductionreaction between a silver halide (and/or an organic silver salt) and areducing agent, a function to accelerate emigration of an image formingsubstance from a light-sensitive layer to an image-receiving material ora image-receiving layer, or a similar function. The image formationaccelerators can be classified into inoragnic bases, organic bases, baseprecursors, oils, surface active agents, hot-melt solvents, and thelike. These groups, however, generally have certain combined functions,i.e., two or more of the above-mentioned effects. Thus, the aboveclassification is for the sake of convenience, and one compound oftenhas a plurality of functions combined.

Various examples of these image formation accelerators are shown below.

Preferred examples of the inorganic bases include hydroxides of alkalimetals or alkaline earth metals; secondary or tertiary phosphates,borates, carbonates, quinolinates and metaborates of alkali metals oralkaline earth metals; a combination of zinc hydroxide or zinc oxide anda chelating agent (e.g., sodium picolinate); ammonium hydroxide;hydroxides of quaternary alkylammoniums; and hydroxides of other metals.Preferred examples of the organic bases include aliphatic amines (e.g.,trialkylamines, hydroxylamines and aliphatic polyamines); aromaticamines (e.g., N-alkyl-substituted aromatic amines,N-hydroxylalkyl-substituted aromatic amines andbis[p-(dialkylamino)phenyl]-methanes), heterocyclic amines, amidines,cyclic amidines, guanidines, and cyclic guanidines. Of these bases,those having a pKa of 7 or more are preferred.

The base precursors preferably are those capable of releasing bases uponreaction by heating, such as salts between bases and organic acidscapable of decarboxylation by heating, compounds capable of releasingamines through intramolecular nucleophilic substitution, Lossenrearrangement, or Beckmann rearrangement, and the like; and thosecapable of releasing bases by electrolysis. Preferred examples of thebase precursors include quanidine trichloroacetate, piperidinetrichloroacetate, morpholine trichloroacetate, p-toluidinetrichloroacetate, 2-picoline trichloroacetate, guanidinephenylsulfonylacetate, guanidine 4-chlorophenylsulfonylacetate,guanidine 4-methyl-sulfonylphenylsulfonylacetate, and4-acetylaminomethyl propionate.

These bases or base precursors are preferably used in an amount of notmore than 100% by weight, and more preferably from 0.1 to 40% by weight,based on the total solid content of the light-sensitive layer. Thesebases or base precursors can be used singly or in combination.

The light-sensitive material employing base or base precursor isdescribed in Japanese Patent Application No. 60(1985)-227528.

Examples of the oils employable in the invention include high-boilingorganic solvents which are used as solvents in emulsifying anddispersing hydrophobic compounds.

Examples of the surface active agents employable in the inventioninclude pyridinium salts, ammonium salts and phosphonium salts asdescribed in Japanese Patent Provisional Publication No. 59(1984)-74547;polyalkylene oxides as described in Japanese Patent ProvisionalPublication No. 59(1984)-57231.

The hot-melt solvents preferably are compounds which may be used assolvent of the reducing agent or those which have high dielectricconstant and can accelerate physical development of silver salts.Examples of the hot-melt solvents include polyethylene glycols,derivatives of polyethylene oxides (e.g., oleate ester), beeswax,monostearin and high dielectric constant compounds having --SO₂ --and/or --CO-- group described in U.S. Pat. No. 3,347,675; polarcompounds described in U.S. Pat. No. 3,667,959; and 1,10-decanediol,methyl anisate and biphenyl suberate described in Research Disclosure26-28 (December 1976). The light-sensitive material employing thehot-melt solvents is described in Japanese Patent Application No.60(1985)-227527. The hot-melt solvent is preferably used in an amount offrom 0.5 to 50% by weight, and more preferably from 1 to 20% by weight,based on the total solid content of the light-sensitive layer.

The thermal polymerization initiators employable in the light-sensitivematerial preferably are compounds that are decomposed under heating togenerate a polymerization initiating species, particularly a radical,and those commonly employed as initiators of radical polymerization. Thethermal polymerization initiators are described in "AdditionPolymerization and Ring Opening Polymerization", 6-18, edited by theEditorial Committee of High Polymer Experimental Study of the HighPolymer Institute, published by Kyoritsu Shuppan (1983). Examples of thethermal polymerization initiators include azo compounds, e.g.,azobisisobutyronitrile, 1,1'-azobis(1-cyclohexanecarbonitrile), dimethyl2,2'-azobisisobutyrate, 2,2'-azobis(2-methylbutyronitrile), andazobisdimethylvaleronitrile; organic peroxides, e.g., benzoyl peroxide,di-tert-butyl peroxide, dicumyl peroxide, tert-butyl hydroperoxide, andcumene hydroperoxide; inorganic peroxides, e.g., hydrogen peroxide,potassium persulfate, and ammonium persulfate; and sodiump-toluenesulfinate. The thermal polymerization initiators are preferablyused in an amount of from 0.1 to 120% by weight, and more preferablyfrom 1 to 10% by weight, based on amount of the polymerizable compound.In a system in which the polymerizable compound located in a portionwhere the latent image has not been formed is polymerized, the thermalpolymerization initiators are preferably incorporated into thelight-sensitive layer. The light-sensitive material employing thethermal polymerization initiators is described in Japanese PatentProvisional Publication No. 61(1986)-260241 (corresponding to U.S. Ser.No. 854,640).

The development stopping agents employable in the light-sensitivematerial are compounds that neutralize a base or react with a base toreduce the base concentration in the layer to thereby stop development,or compounds that mutually react with silver or a silver salt tosuppress development. More specifically, examples of the developmentstopping agents include acid precursors capable of releasing acids uponheating electrophilic compounds capable of undergoing substitutionreaction with a coexisting base upon heating, nitrogen-containingheterocyclic compounds, mercapto compounds, and the like. Examples ofthe acid precursors include oxide esters 5 described in Japanese PatentProvisional Publication Nos. 60(1985)-108837 and 60(1985)-192939 andcompounds which release acids through Lossen rearrangement described inJapanese Patent Provisional Publication No. 60(1985)-230133. Examples ofthe electrophilic compounds which induce substitution reaction withbases upon heating are described in Japanese Patent ProvisionalPublication No. 60(1985)-230134.

The antismudging agents employable in the light-sensitive materialpreferably are particles which are solid at ambient temperatures.Examples of the antismudging agents include starch particles describedin U.K. Patent No. 1,232,347; polymer particles described in U.S. Pat.No. 3,625,736; microcapsule particles containing no color formerdescribed in U.K. Patent No. 1,235,991; and cellulose particles, andinorganic particles, such as particles of talc, kaolin, bentonite,agalmatolite, zinc oxide, titanium oxide or almina described in U.S.Pat. No. 2,711,375. Such particles preferably have a mean size of 3 to50 μm, more preferably 5 to 40 μm. When the microcapsule is employed inthe light-sensitive material, the size of said particle is preferablylarger than that of the microcapsule.

Binders employable in the light-sensitive material preferably aretransparent or semi-transparent hydrophilic binders. Examples of thebinders include natural substances, such as gelatin, gelatinderivatives, cellulose derivatives, starch, and gum arabic; andsynthetic polymeric substances, such as water-soluble polyvinylcompounds e.g., polyvinyl alcohol, polyvinylpyrrolidone, and acrylamidepolymers. In addition to the synthetic polymeric substances, vinylcompounds dispersed in the form of latex, which are particularlyeffective to increase dimensional stability of photographic materials,can be also used. These binders can be used singly or in combination.The light-sensitive material employing a binder is described in JapanesePatent Provisional Publication No. 61(1986)-69062.

Examples and usage of the other optional components which can becontained in the light-sensitive layer are also described in theabove-mentioned publications and applications concerning thelight-sensitive material, and in Research Disclosure Vol. 170, No.17029, 9-15 (June 1978).

Examples of auxiliary layers which are optionally arranged on thelight-sensitive material include an image-receiving layer, a heatinglayer, an antistatic layer, an anticurl layer and a release layer.

Instead of the use of the image-receiving material, the image-receivinglayer can be arranged on the light-sensitive material to produce thedesired image on the on the image-receiving layer of the light-sensitivematerial. The image-receiving layer of the light-sensitive material canbe constructed in the same manner as the layer of the image-receivingmaterial. The details of the image-receiving layer will be describedlater.

The light-sensitive material employing the heating layer is described inJapanese Patent Application No. 60(1985)-135568. Examples and usage ofthe other auxiliary layers are also described in the above-mentionedpublications and applications concerning the light-sensitive material.

The light-sensitive material of the invention can be prepared, forinstance, by the following process.

The light-sensitive material is usually prepared by dissolving,emulsifying or dispersing each of the components of the ligt-sensitivelayer in an adequate medium to obtain coating solution, and then coatingthe obtained coating solution on a support.

The coating solution can be prepared by mixing liquid compositions eachcontaining a component of the light-sensitive layer. Liquid compositioncontaining two or more components may be also used in the preparation ofthe coating solution. Some components of the light-sensitive layer canbe directly added to the coating solution or the liquid composition.Further, a secondary composition can be prepared by emulsifying the oily(or aqueous) composition in an aqueous (or oily) medium to obtain thecoating solution.

In preparation of the light-sensitive material, the polymerizablecompounds are used as the medium for preparation of the liquidcomposition containing another component of the light-sensitive layer.For example, the silver halide (including the silver halide emulsion),the reducing agent, or the color image forming substance can bedissolved, emulsified or dispersed in the polymerizable compound toprepare the light-sensitive material. Especially, the color imageforming substance is preferably incorporated in the polymerizablecompound. Further, the necessary components for preparation of amicrocapsule, such as shell material can be incorporated into thepolymerizable compound.

The light-sensitive composition which is the polymerizable compoundcontaining the silver halide can be prepared using the silver halideemulsion. The light-sensitive composition can be also prepared usingsilver halide powders which can be prepared by lyophilization. Theselight-sensitive composition can be obtained by stirring thepolymerizable compound and the silver halide using a homogenizer, ablender, a mixer or other conventional stirring device.

Polymers having a principal chain consisting essentially of ahydrocarbon chain substituted in part with hydrophilic groups whichcontain, in their terminal groups. --OH or nitrogen having a loneelectron-pair are preferably introduced into the polymerizable compoundprior to the preparation of the light-sensitive composition. The polymerhas a function of dispersing silver halide or other component in thepolymerizable compound very uniformly as well as a function of keepingthus dispered state. Further, the polymer has another function ofgathering silver halide along the interface between the polymerizablecompound (i.e., light-sensitive composition) and the aqueous medium inpreparation of the microcapsule. Therefore, using this polymer, silverhalide can be easily introduced into the shell material of themicrocapsule.

The polymerizable compound (including the light-sensitive composition)are preferably emulsified in an aqueous medium to prepare the coatingsolution. The necessary components for preparation of the microcapsule,such as shell material can be incorporated into the emulsion. Further,other components such as the reducing agent can be added to theemulsion.

The emulsion of the polymerizable compound can be processed for formingshell of the microcapsule. Examples of the process for the preparationof the microcapsules include a process utilizing coacervation ofhydrophilic wall-forming materials as described in U.S. Pat. Nos.2,800,457 and 2,800,458; an interfacial polymerization process asdescribed in U.S. Pat. No. 3,287,154, U.K. Patent No. 990,443 andJapanese Patent Publication Nos. 38(1963)-19574, 42(1967)-446 and42(1967)-771; a process utilizing precipitation of polymers as describedin U.S. Pat. Nos. 3,418,250 and 3,660,304; a process of usingisocyanate-polyol wall materials as described in U.S. Pat. No.3,796,669; a process of using isocyanate wall materials as described inU.S. Pat. No. 3,914,511; a process of using urea-formaldehyde orurea-formaldehyde-resorcinol wall-forming materials as described in U.S.Pat. Nos. 4,001,140, 4,087,376 and 4,089,802; a process of usingmelamineformaldehyde resins hydroxypropyl cellulose or like wall-formingmaterials as described in U.S. Pat. No. 4,025,455; an in situ processutilizing polymerization of monomers as described in U.K. Patent No.867,797 and U.S. Pat. No. 4,001,140; an electrolytic dispersion andcooling process as described in U.K. Patent Nos. 952,807 and 965,074; aspray-drying process as described in U.S. Pat. No. 3,111,407 and U.K.Patent 930,422; and the like. It is preferable, though not limitative,that the microcapsule is prepared by emulsifying core materialscontaining the polymerizable compound and forming a polymeric membrane(i.e., shell) over the core materials.

When the emulsion of the polymerizable compound (including thedispersion of the microcapsule) has been prepared by using thelight-sensitive composition, the emulsion can be used as the coatingsolution of the light-sensitive material. The coating solution can bealso prepared by mixing the emulsion of the polymerizable compound andthe silver halide emulsion.

A light-sensitive material of the invention can be prepared by coatingand drying the above-prepared coating solution on a support in theconventional manner.

Use of the light-sensitive material is described below.

In the use of the light-sensitive material of the invention, adevelopment process is conducted simultaneously with or after animagewise exposure.

Various exposure means can be employed in the image-wise exposure, andin general, the latent image on the silver halide is obtained byimagewise exposure to radiation including visible light. The type oflight source and exposure can be selected depending on thelight-sensitive wavelengths determined by spectral sensitization orsensitivity of silver halide. Original image can be either monochromaticimage or color image.

Development of the light-sensitive material can be conductedsimultaneously with or after the imagewise exposure. The development canbe conducted using a developing solution in the same manner as the imageforming method described in Japanese Patent Publication No.45(1970)-11149. The image forming method described in Japanese PatentProvisional Publication No. 61(1986)-69062 which employs a heatdevelopment process has an advantage of simple procedures and shortprocessing time because of the dry process. Thus, the latter method ispreferred as the development process of the light-sensitive material.

Heating in the heat development process can be conducted in variousknown manners. The heating layer which is arranged on thelight-sensitive material can be used as the heating means in the samemanner as the light-sensitive material described in Japanese PatentApplication No. 60(1985)-135568. Heating temperatures for thedevelopment process usually ranges from 80° C. to 200° C. and preferablyfrom 100° C. to 160° C. Various heating patterns are applicable. Theheating time is usually from 1 second to 5 minutes, and preferably from5 seconds to 1 minute.

During the above development process, a polymerizable compound in aportion where a latent image of the silver halide has been formed or ina portion where a latent image of the silver halide has not been formedis polymerized. In a general system, the polymerizable compound in aportion where the latent image has been formed is polymerized. If anature or amount of the reducing agent is controlled, the polymerizablecompound in a portion where the latent image has not been formed can bepolymerized in the same manner as the light-sensitive material describedin Japanese Patent Provisional Publication No. 61(1986)-260241(corresponding to U.S. patent Ser. No. 854,640).

In the above development process, a polymer image can be formed on thelight-sensitive layer. A pigment image can be also obtained by fixingpigments to the polymer image.

The image can be also formed on the image-receiving material. Theimage-receiving material is described hereinbelow. The image formingmethod employing the image-receiving material or the image-receivinglayer is described in Japanese Patent Provisional Publication No.61(1986)-278849 (corresponding to U.S. patent Ser. No. 868,385).

Examples of the material employable as the support of theimage-receiving material include baryta paper in addition to variousexamples which can be employed as the support of the knownlight-sensitive material.

The image-receiving material is usually prepared by providing theimage-receiving layer on the support. The image-receiving layer can beconstructed according to the color formation system. In the cases that apolymer image is formed on the image-receiving material and that a dyeor pigment is employed as the color image forming substance, theimage-receiving material be composed of a simple support.

For example, when a color formation system using a color former anddeveloper is employed, the developer can be contained in theimage-receiving layer. Further, the image-receiving layer can becomposed of at least one layer containing a mordant. The mordant can beselected from the compounds known in the art of the conventionalphotography according to the kind of the color image forming substance.If desired, the image-receiving layer can be composed of two or morelayers containing two or more mordants different in the mordanting powerfrom each other.

The image-receiving layer preferably contains a polymer as binder. Thebinder which may be employed in the above-mentioned light-receivinglayer is also employable in the image-receiving layer.

The image-receiving layer can be composed of two or more layersaccording to the above-mentioned functions. The thickness of theimage-receiving layer preferably ranges from 1 to 100 μm, morepreferably from 1 to 20 μm.

After the development process, pressing the light-sensitive material incontact with the image-receiving material to transfer the polymerizablecompounds which is still polymerizable to the image-receiving material,a polymer image can be obtained in the image-receiving material. Theprocess for pressing can be carried out in various known manners.

In the case that the light-sensitive layer contains a color imageforming substance, the color image forming substance is fixed bypolymerization of the polymerizable compound. Then, pressing thelight-sensitive material in contact with the image-receiving material totransfer the color image forming substance in unfixed portion, a colorimage can be produced on the image-receiving material.

The light-sensitive material can be used for monochromatic or colorphotography, printing, radiography, diagnosis (e.g., CRT photography ofdiagnostic device using supersonic wave), copy (e.g., computer-graphichard copy), etc.

The present invention is further described by the following exampleswithout limiting the invention.

EXAMPLE 1 Preparation of silver halide emulsion

In 1,000 ml of water were dissolved 20 g of gelatin and 1 g of potassiumbromide, and the resulting gelatin solution was kept at 60° C. To thegelatin solution, 600 ml of an aqueous solution containing 70 g ofpotassium bromide and 600 ml of an aqueous solution containing 0.59 moleof silver nitrate were added simultaneously at the same feed rate over aperiod of 40 minutes. Further, after 5 mimutes, to the resulting mixturewas added 100 ml of an aqueous solution containing 2 g of potassiumiodide to obtain a silver iodobromide emulsion having cubic grains,uniform grain size distribution and a mean grain size of 0.20 μm. All ofthe silver halide grains have an aspect ratio of not more than 5. Theshell was 2% of the silver halide grain based on the silver content. Thesilver iodide content in the core was 0%, and the silver iodide contentin the shell was 100%.

The emulsion was washed for desalting to obtain a silver halide emulsion(a). The yield of the emulsion was 600 g.

Preparation of silver benzotriazole emulsion

In 3,000 ml of water were dissolved 28 g of gelatin and 13.2 g ofbenzotriazole, and the solution was kept at 40° C. while stirring. Tothe solution was added 100 ml of an aqueous solution of 17 g of silvernitrate over 2 min. Excessive salts were sedimented and removed from theresulting emulsion by pH-adjustment. Thereafter, the emulsion wasadjusted to a pH of 6.30 to obtain a silver benzotriazole emulsion. Theyield of the emulsion was 400 g.

Preparation of light-sensitive composition

In 100 g of trimethylolpropane triacrylate were dissolved 0.40 g of thefollowing copolymer, 6.00 g of Pargascript Red I-6-B (produced by CibaGeigy) and 2 g of Emulex NP-8 (tradename, produced by Nippon EmulsionCo., Ltd.). ##STR1##

To 2 g of the resulting solution was added a solution in which 0.16 g ofthe following reducing agent (I) and 1.22 g of the following reducingagent (II) are dissolved in 1.80 g of methylene chloride. ##STR2##

Further, to the resulting solution were added 2 g of the silver halideemulsion and 2 g of the silver benzotriazole emulsion, and the mixturewas stirred at 15,000 r.p.m. for 5 min. to obtain a light-sensitivecomposition.

Preparation of light-sensitive microcapsule

To 10.51 g of 18.6% aqueous solution of Isobam (tradename, produced byKuraray Co., Ltd.) was added 48.56 g of 2.89% aqueous solution ofpectin. After the solution was adjusted to a pH of 4.0 using 10%sulfuric acid, the light-sensitive composition was added to theresulting solution, and the mixture was stirred at 7,000 r.p.m. for 2min. using a homogenizer to emulsify the light-sensitive composition inthe aqueous medium.

To 72.5 g of the aqueous emulsion were added 8.32 g of 40% aqueoussolution of urea, 2.82 g of 11.3% aqueous solution of resorcinol, 8.56 gof 37% aqueous solution of formaldehyde, and 2.74 g of 8.76% aqueoussolution of ammonium sulfate in this order, and the mixture was heatedat 60° C. for 2 hours while stirring. After the mixture was adjusted toa pH of 7.0 using 10% aqueous solution of sodium hydroxide, 3.62 g of30.9% aqueous solution of sodium hydrogen sulfite was added to themixture to obtain a dispersion containing light-sensitive microcapsules.

Preparation of light-sensitive material

To 10.0 g of the light-sensitive microcapsule dispersion were added 1.0g of 1% aqueous solution of the following anionic surfactant and 3.0 gof 10% solution (solvent: water/ethanol=50/50 as volume ratio) ofguanidine trichroloacetate to prepare a coating solution. ##STR3##

The coating solution was uniformly coated on a polyethyleneterephthalatefilm (thickness: 100 μm) using a coating rod of #40 to a wet thicknessof 70 μm and dried at about 40° C. to obtain a light-sensitive material(A).

EXAMPLE 2 Preparation of silver halide emulsion

The silver emulsion (a) prepared in Example 1 was subjected to chemicalsensitization with 5 mg of sodium thiosulfate and 20 mg of4-hydroxy-6-methyl-1,3,3a,7-tetraazaindenetetraazaindene at 60° C. toobtain a silver halide emulsion (b).

Preparation of light-sensitive material

A light-sensitive material (B) was prepared in the same manner as inExample 1 except that the above silver halide emulsion (b) was used.

COMPARISON EXAMPLE 1 Preparation of silver halide emulsion

In 1,000 ml of water were dissolved 20 g of gelatin and 3 g of sodiumbromide, and the resulting gelatin solution was kept at 50° C. To thegelatin solution, 600 ml of an aqueous solution containing 21 g ofsodium chloride and S5 g of potassium bromide and 600 ml of an aqueoussolution containing 0.59 mole of silver nitrate were addedsimultaneously at the same feed rate over a period of 20 minutes toobtain a silver chlorobromide emulsion having cubic grains, uniformgrain size distribution, a mean grain size of 0.20 μm and a bromidecontent of 50 mole %. All of the silver halide grains have an aspectratio of not more than 5.

The emulsion was washed for desalting and then subjected to chemicalsensitization with 5 mg of sodium thiosulfate and 20 mg of4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene at 60° C. to obtain a silverhalide emulsion (c). The yield of the emulsion was 600 g.

Preparation of light-sensitive material

A light-sensitive material (C) was prepared in the same manner as inExample 1 except that the above silver halide emulsion (c) was used.

EXAMPLE 3 Preparation of silver halide emulsion

Each of silver halide emulsions (d) to (k) having cubic grains, uniformgrain size distribution and a mean grain size of 0.20 μm was prepared inthe same manner as in Example 1 except that each of the grain formationwas adjusted to the ratio of the shell to the silver halide grain andthe silver iodide contents in the core and in the shell set forth inTable 1. All of the silver halide grains contained in each of the silverhalide emulsions (d) to (k) have an aspect ratio of not more than 5.

Preparation of light-sensitive material

Light-sensitive materials (D) to (K) were prepared in the same manner asin Example 1 except that the silver halide emulsions (d) to (k) wererespectively used.

COMPARISON EXAMPLE 2 Preparation of silver halide emulsion

A silver halide emulsion (1) having cubic grains, uniform grain sizedistribution and a mean grain size of 0.20 μm was prepared in the samemanner as in Example 1 except that the grain formation was adjusted tothe ratio of the shell to the silver halide grain and the silver iodidecontents in the core and in the shell set forth in Table 1. All of thesilver halide grains have an aspect ratio of not more than 5.

Preparation of light-sensitive material

A light-sensitive material (L) was prepared in the same manner as inExample 1 except that the above silver halide emulsions (1) was used.

                  TABLE 1                                                         ______________________________________                                                   Shell/Silver                                                                  Halide Grain   Silver                                              Silver Halide                                                                            (Based on      Iodide Content                                      Emulsion   Silver Content)                                                                              Core   Shell                                        ______________________________________                                        (a)        2%             0%     100%                                         (d)        0.01%          0%     100%                                         (e)        0.1%           0%     100%                                         (f)        10%            0%     100%                                         (g)        50%            0%     100%                                         (h)        2%             0%      50%                                         (i)        2%             0%      10%                                         (j)        2%             10%    100%                                         (k)        2%             10%     50%                                         (l)        2%             50%     10%                                         ______________________________________                                    

COMPARISON EXAMPLE 3 Preparation of silver halide emulsion

In 1,000 ml of water were dissolved 20 g of gelatin and 1 g of potassiumbromide, and the resulting gelatin solution was kept at 60° C. To thegelatin 600 ml of an aqueous solution containing 70 g of potassiumbromide and 600 ml of an aqueous solution 0.5g mole of silver nitratewere added simultaneous the same feed rate over a period of 40 minutesto obtain a silver bromide emulsion having cubic grains, uniform grainsize distribution and a mean grain size of 0.20 μm. All of the silverhalide grains have an aspect ratio of not more than 5.

The emulsion was washed for desalting to obtain a silver halide emulsion(m). The yield of the emulsion was 600 g.

Preparation of light-sensitive material

A light-sensitive material (M) was prepared in the same manner as inExample 1 except that the above silver halide emulsion (m) was used.

EXAMPLE 4 Preparation of light-sensitive material

A light-sensitive material (N) was prepared in the same manner as inExample 1 except that the silver benzotriazole emulsion was not used.

COMPARISON EXAMPLE 4 Preparation of light-sensitive material

A light-sensitive material (O) was prepared in the same manner as inExample 1 except that the silver halide emulsion (c) prepared inComparison Example 1 was used and the silver benzotriazole emulsion wasnot used.

Preparation of image-receiving material

To 125 g of water was added 11 g of 40% aqueous solution of sodiumhexametaphosphate, and were further added 34 g of zinc3,5-di-α-methylbenzylsalicylate and 82 g of 55% slurry of calciumcarbonate, followed by coarsely dispersing in a mixer. The coarsedispersion was then finely dispersed in a dynamic dispersing device. To200 g of the resulting dispersion were added 0 g of 50% latex of SBR(styrene-butadiene rubber) and 55 g of 8% aqueous solution of polyvinylalcohol, and the resulting mixture was made uniform.

The mixture was then uniformly coated on an art paper having a weight of43 g/m² to give a layer having a wet thickness of 30 μm and dried toobtain an imagereceiving material.

Evaluation of light-sensitive material

Each of the light-sensitive materials prepared in Examples 1 to 5 andComparison Examples 1 to 4 was imagewise exposed to light through afilter in which the density continuously changed, using a tungsten lampat 200 lux for 1 second and then heated on a hot plate at 125° C. for 30seconds. Each of the exposed and heated light-sensitive materials wasthen combined with the image-receiving material and passed through pressrolls under pressure of 350 kg/cm² to obtain a magenta positive image onthe image receiving material. The density of the obtained image wasmeasured using Macbeth reflection densitometer.

The results are set forth in Table 2. In Table 2, "Relative Sensitivity"is referred to a relative value based on the sensitivity (100) of thelight-sensitive material (M), and each of "Mimimum Density" and "MaximumDensity" is respectively referred to the increase or decrease over thevalue of the light-sensitive material (M)

                  TABLE 2                                                         ______________________________________                                        Light- Silver   Silver*  Relative                                             Sensitive                                                                            Halide   Benzo-   Sensi- Minimum                                                                              Maximum                                Material                                                                             Emulsion triazole tivity Density                                                                              Density                                ______________________________________                                        (A)    (a)      +        236    -0.08  +0.22                                  (B)    (b)      +        270    -0.11  +0.15                                  (C)    (c)      +         75    +0.02  -0.05                                  (D)    (d)      +        109    -0.01  +0.02                                  (E)    (e)      +        169    -0.05  +0.10                                  (F)    (f)      +        221    -0.08  +0.19                                  (G)    (g)      +        173    -0.05  +0.11                                  (H)    (h)      +        210    -0.07  +0.17                                  (I)    (i)      +        180    -0.06  +0.12                                  (J)    (j)      +        266    -0.11  +0.26                                  (K)    (k)      +        203    -0.07  +0.16                                  (L)    (l)      +         83    +0.02  +0.04                                  (M)    (m)      +        100    Standard                                                                             Standard                               (N)    (a)      -        229    -0.09  +0.24                                  (O)    (c)      -         68    +0.02  -0.01                                  ______________________________________                                         Remark *"Silver Benzotriazole" indicates whether the lightsensitive           material contains silver benzotriazole (+) or not (-).                   

It is apparent from the results in Table 2 that each of thelight-sensitive materials (A), (B), and (D) to (K) of the inventionforms a clear positive image which has a high maximum density and a lowminimum density. It is also apparent that the same effect can beexpected regardless of the addition of the silver benzotriazole emulsion(see the line of the material (N) in Table 2), and the material (N)containing no silver benzotriazole emulsion forms a more clear imagewhich has a higher maximum density.

I claim:
 1. An image-forming method which comprises the stepsof:imagewise exposing to light a light-sensitive element comprising asupport and a light-sensitive layer which contains silver halide grains,a reducing agent and an ethylenic unsaturated polymerizable compound,said silver halide grains being contained in such amount that the totalsilver content in the light-sensitive layer is in the range of from 0.1mg/m² to 10 g/m², said reducing agent being contained in the range offrom 0.1 to 1,500 mole % based on the total silver content in thelight-sensitive layer, and said polymerizable compound being containedin the range of from 5 to 120,000 times by weight as much as the amountof the silver halide grains; and simultaneously or thereafter heatingthe light-sensitive element at a temperature in the range of 80° C. to200° C. to imagewise polymerize the polymerizable compound, wherein thesilver halide grains have a mean grain size of 0.001 to 5 μm and atleast 50% of number of the silver halide grains have an aspect ratio ofnot more than 5 and have such a core/shell structure that the shellportion contains iodine at a concentration higher than that in the coreportion, the iodine concentration in the shell portion is not less than10 mold % of the halogen content therein, and the shell portion containssilver in an amount of 0.01 to 50 weight % of the silver in the silverhalide grains.
 2. The image-forming method as claimed in claim 1,wherein the polymerizable compound is polymerized within the area wherethe latent image of the silver halide has been formed.
 3. Theimage-forming method as claimed in claim 1, wherein after heating thelight-sensitive element, the light-sensitive element is pressed on animage-receiving element to transfer the obtained image to theimage-receiving element.
 4. The image-forming method as claimed in claim1, wherein the light-sensitive element is heated at a temperature in therange of 100° C. to 160° C.
 5. The image-forming method as claimed inclaim 1, wherein the iodine concentration in the shell portion is notless than 30 mole % of the halogen content therein.
 6. The image-formingmethod as claimed in claim 1, wherein the iodine concentration in thewhole silver halide grains is not more than 50 mole % of the halogencontent therein.
 7. The image-forming method as claimed in claim 1,wherein the shell portion contains silver in an amount of 0.1 to 50weight % of the silver in the silver halide grains.
 8. The image-formingmethod as claimed in claim 1, wherein the silver halide grains have amean grain size of 0.01 to 0.5 μm.
 9. The image-forming method asclaimed in claim 1, wherein at least 70% of number of the silver halidegrains have an aspect ratio of not more than
 5. 10. The image-formingmethod as claimed in claim 1, wherein the silver halide grains have anaverage aspect ratio of not more than
 5. 11. The image-forming method asrecited in claim 1, wherein the different between the iodineconcentration of the shell portion and that in the core potion is largerthan 2 mole %.
 12. The image-forming method as claimed in claim 1,wherein the different between the iodine concentration of the shellportion and that in the core portion is larger than 10 mole %.
 13. Theimage-forming method as claimed in claim 1, wherein the light-sensitivelayer further contains a color image forming substance, said color imageforming substance being contained in an amount of from 0.5 to 50 weight% based on the amount of the polymerizable compound.
 14. Theimage-forming method as claimed in claim 1, wherein the silver halidegrains and polymerizable compound are contained in microcapsules whichare dispersed in the light-sensitive layer.
 15. The image-forming methodas claimed in claim 1, wherein the silver halide grains andpolymerizable compound are contained in microcapsules which aredispersed in the light-sensitive layer, at least 70% of said silverhalide grains being arranged in the shell of the microcapsules or on theinner surface of the shell of the microcapsules.
 16. The image-formingmethod as claimed in claim 1, wherein the silver halide grains andpolymerizable compound are contained in microcapsules which aredispersed in the light-sensitive layer, and microcapsules having a meansize in the range of from 0.5 to 50 μm.